The present invention relates to partially hydrophilicized silica gel in which the pore inside is hydrophobicized and the external surface has silanol groups or hydrophilic organic groups, and to a process for producing the same.
Heretofore, silica gel has found a variety of uses as adsorbent, drying agent, catalyst carrier, etc. by virtue of its porosity and the active silanol groups present on its surface. In the field of analysis, it is used as a carrier or packing for liquid chromatography.
In liquid chromatography, silica gel is generally used as a carrier for normal phase chromatography. Silica gel strongly adsorbs water and other polar solvents and ionic compounds such as amino acids because there are silanol groups on its surface as mentioned above; therefore, it is necessary to protect the silanol groups where such polar solvents are used and highly ionic compounds are to be separated. The protection of silanol groups has been accomplished by introducing an alkylsilyl group, particularly octadecylsilyl group, into them. Silica gel with an alkyl group is used for reversed phase chromatography that employs a polar solvent. The silica gel into which a hydrophobic alkyl group is introduced is characterized by that the entire surface including the pore inside is hydrophobicized by the introduction of an alkyl group. There has been no silica gel in which the hydrophobic group is introduced into a part of the entire surface or the hydrophobic group is introduced into a part of the surface and the hydrophilic organic group is introduced into the rest of the surface.
Recently, there are many instances in the medical and pharmaceutical fields where it is necessary to determine a trace amount of components coexistent with proteins, for example, drugs in serum. If a component coexistent with proteins is to be analyzed by reversed phase chromatography, it is necessary to perform pretreatment for the removal of proteins. The pretreatment is accomplished by adding ammonium chloride to a sample containing proteins, whereby adjusting the pH and precipitating proteins. The precipitates of proteins are centrifugally removed. This pretreatment is necessary because when a protein-containing sample comes into contact with the silica gel having the above-mentioned octadecylsilyl group introduced thereinto, the protein is absorbed and precipitated on the surface of the silica gel. The precipitation and centrifugal removal of proteins need complex and time-consuming procedures, and the precipitation of proteins involves the possibility of coprecipitating the components to be determined. For this reason, there has been a demand for a simple method of analyzing components coexistent with proteins.